1. Field of the Invention
The present invention relates to an apparatus for transferring objects in a processing system. More particularly, the present invention relates to a robot for effecting substrate exchange using a single stroke and multiple extended positions of the robot.
2. Background of the Related Art
The advantages of using robots in the production of integrated circuits to transfer substrates through a processing system are well established. Current practice includes the use of a robot disposed in a central transfer chamber to move substrates from a loading port into various chambers mounted on the transfer chamber. Various robot designs, including frog-leg type and single-arm type, are currently employed in commercial processing systems. Typically, a robot blade having a substrate supporting surface is attached to the end of a pair of robot arms to provide a substrate supporting surface to carry the substrate through the processing system. The robot arm can retrieve a substrate from a particular chamber, such as a load lock chamber, and shuttle the substrate into another chamber, such as a processing chamber. When substrate processing is complete, the robot arm retrieves the substrate from the processing chamber and returns the substrate to the load lock chamber and another substrate is then moved into the processing chamber. Typically, several substrates are handled in this manner during each process run, and several substrates are passed through the system during a single process cycle.
In multiple chamber process systems, it is desirable to increase the substrate throughput of the system by concurrently processing substrates in each of the chambers. A typical substrate handling sequence used in multiple chamber processing systems includes removing a substrate from a process chamber, moving the substrate to the next processing chamber or storing the substrate in a selected location, and then moving a new substrate from a storage location into the processing chamber from which the first substrate was removed. In this sequence of robot movements, the robot arm itself goes through significant repetitive rotations, extensions and retractions to simply exchange substrates within a selected chamber.
To increase the efficiency of substrate handling, a robot arm having the ability to handle two substrates at the same time on opposed sides of a robot has been employed. For example, FIG. 1a shows a robot 2 including two pair of struts 4 and 5 having robot blades 6 and 7 mounted thereto. The struts 4 and 5 are pivotally connected to a pair of drive arms 9 which are rotated about a pivot 8. One substrate is stored on the blade 7 while the opposite blade 6 is used to retrieve a substrate from the location in which the substrate exchange is to occur. Once the processed substrate is retrieved from the processing chamber by blade 7, the robot rotates 180.degree. and the substrate disposed on blade 6 may be placed in the processing chamber. The robot then rotates again to place the processed substrate back into the load lock chamber, a storage chamber or in another processing chamber. While this robot configuration reduces the chamber idle time by providing a substrate following the 180.degree. rotation, it does not allow for the immediate replacement of a new substrate in a process chamber after a processed substrate is removed. Additionally, this configuration is still limited to delivering or retrieving a substrate in a single chamber on any given extension.
In another attempt to increase throughput and decrease chamber idle time associated with substrate transfer, another robot configuration provides for linked, coordinated movement of two blades 30 and 30' on separate planes as shown in FIG. 1b. Two concentric hubs 12 and 12' drive a linkage connecting blades 30 and 30' thereto. Dual plane robots can perform a shuttle operation which decreases chamber idle time. In addition, the time that the slit valve must remain open while the robot transfers a first substrate out of the chamber and inserts a second substrate into the chamber is also decreased. As a result, the throughput of the system can be increased and the period of time in which particles present outside the chamber may enter into the chamber can be decreased. However, this configuration still requires full-length strokes to accomplish insertion and retraction by each set of the robot arms to effect substrate exchange.
Another attempt to increase throughput and effect wafer exchange is illustrated in FIG. 1c and includes a blade configuration which can increase throughput by effecting substrate exchange using a single stroke and multiple positions of the robot. This linkage is described in U.S. patent application Ser. No. 08/946,920, entitled "Robot Blade With Dual Offset Wafer Supports," filed Oct. 8, 1997, which is hereby incorporated in its entirety by reference. Generally, the wafer blade defines a pair of spaced parallel wafer supporting surfaces 38 and 38' which are offset by a vertical and horizontal distance, D1 and D2 respectively, so that the upper supporting surface extends over the lower supporting surface. This offset allows lift pins disposed in a wafer support to independently access wafers supported on each of the support surfaces without any interference therebetween. Using the robot blade with the dual offset wafers supports, a wafer may be transferred from the chamber onto one of the wafer supporting surfaces and then a wafer disposed on the other wafer supporting surface may be transferred into the chamber during a single stroke of insertion and retraction by robot. The robot need only to make a small radial movement to support the second substrate supporting surface over the lift pins.
Unfortunately, the offset wafer supporting surfaces require a deeper stroke of the wafer blade into the process chamber because to align the lower support surface with the lifting pins the upper support surface must be moved further into the process chamber. In order to accommodate the deeper stroke of the wafer blade, the process chamber must be redesigned and its cavity made larger. However, redesigning the process chamber to accommodate the deeper stroke is relatively costly and may affect process uniformity or require a larger process chamber.
Thus, there remains a need for a robot having minimal parts that can perform a substrate shuttle operation with minimal movements.